braking issue - bad master cylinder out of the box?

[hedz]

i don't see any busted wheel cylinders but the pedal is going half way down now and isn't braking as hard. i have a feeling i need a quality master cylinder, quality booster, and quality front wheel cylinders.

i have a 95 astrovan hydroboost and a master cylinder from a 79 big body lincoln with hydroboost. i have pushrods for both setups. i'm thinking hydroboost on drums again...

[ultraranger]

If the brakes were serviced recently with good pedal pressure/feel and now, only a couple of weeks later the pedal is mushy, there is either air still in the system, the booster is defective or you have a fluid leak.

Check all line connections and make sure they're not wet with brake fluid. Also check where the MC attaches to the front of the booster. If the MC is leaking out the back, this will make the pedal sink. The other bad part about this is if it's leaking out the back, it's probably getting brake fluid into the booster which will destroy the booster diaphragm.

I'm not aware of any hydroboost system that was factory installed on a vehicle with front drums. Drum brakes are self-energizing (discs are not). A much more powerful booster, such as a hydroboost, may make the brakes overly sensitive when you go to apply the brake pedal, if drums remain on the front.

....on the subject of hydroboost, this is an interesting hydroboost installation on a first generation (1966-1977) Bronco.

http://www.emotoman.com/4x4/hydroboost/hydroboost.html

[hedz]

If the brakes were serviced recently with good pedal pressure/feel and now, only a couple of weeks later the pedal is mushy, there is either air still in the system, the booster is defective or you have a fluid leak.

Check all line connections and make sure they're not wet with brake fluid. Also check where the MC attaches to the front of the booster. If the MC is leaking out the back, this will make the pedal sink. The other bad part about this is if it's leaking out the back, it's probably getting brake fluid into the booster which will destroy the booster diaphragm.

I'm not aware of any hydroboost system that was factory installed on a vehicle with front drums. Drum brakes are self-energizing (discs are not). A much more powerful booster, such as a hydroboost, may make the brakes overly sensitive when you go to apply the brake pedal, if drums remain on the front.

....on the subject of hydroboost, this is an interesting hydroboost installation on a first generation (1966-1977) Bronco.

http://www.emotoman.com/4x4/hydroboost/hydroboost.html

i have commented on this hydroboost write up before. it is a terrible example and i highly discourage it. mercury grand marquis hydroboost is not the way to go. i played around with one. i know. he lucked out and got all his parts so good for him.

also hydroboost works excellent on 4 wheel drum setups. ive seen it done with multiple hydroboost models.

in 1 months time i have had 2 master cylinders fail, 1 from autozone, 1 from oreillys, and all 4 wheel cylinders have now failed from oreillys. f100 is on jack stands. tracking down vacuum bleeding pump tomorrow and wheel cylinders from napa to match the brand new napas on the rear and am wiping my hands free of oreillys and autozone and all these other jokers.

oreillys and autozone are the equivelant of a payday loan outlet. nuff said

[motzingg]

i'm back to this problem again myself. glad to here its not just me.

i had my brakes go out on me the other day and finally got my ass in gear to replace the rear wheel cylinders (which were leaking at a pretty good rate)

I got the rears done at about 11 pm after 3 trips to various auto parts stores to piece together a complete hardware kit (40 bucks, all because oreily was sold out of the 17 dollar 'complete kit) and having my drums turned, etc.

got it all done and still crummy brakes, turns out the check valve in the MC has gone out on the front wheels so only the back have been stopping this entire time.


I ordered a raybestos new not reman, MC from rock auto, we'll see when it gets here if its worth a damn.

I'm sure the fact that we are all dealing with crusty, grimey lines that haven't been flushed in 50 years couldn't have anything to do with the check valve failures, could it?

When i redid my rears, i hooked up a vac pump and pulled vac on them for about a half hour each side, they were pretty clean as i've been pumping brand new fluid through them at the rate of about 1 pint every 2 months.

the fronts are still backwashing some filth into the reservoir so i'm fairly certain that is the problem, and not the china reman'd MC.

[ultraranger]

I ordered a raybestos new not reman, MC from rock auto, we'll see when it gets here if its worth a damn.

I'm sure the fact that we are all dealing with crusty, grimey lines that haven't been flushed in 50 years couldn't have anything to do with the check valve failures, could it?

Lack of brake maintenance (not changing the brake fluid) on a regular basis is a big problem of why brake components fail, stock brake valves stick, brakes malfunction, etc.

DOT 3, 4 or 5.1 brake fluid needs to be changed every 18 to 24 months. Not only does this help keep sediment to a minimum, it keeps the moisture level down that the brake fluid continually absorbs over time.

Many of the parts stores replacement brake MCs don't come with RPVs (Residual Pressure Valves) installed in the ports that supply fluid to a drum brake circuit. --even if the original MC did. Fluid contamination, dirt, rust, debris and moisture are all things that can clog RPVs . Probably the biggest reason most MCs today don't come with them are for these reasons.

The industry has gone more to cup expanders in the wheel cylinders. They are cheaper to produce than an RPV, easier to install and they don't get clogged up with debris.

The industry has also gotten away from the old conventional style cast iron MC with the large removable tops. Iron rusts and the MC is mounted higher than the drum/drum pressure differential or disc/drum combination valves. The first place rust contaminants deposit in, from an iron MC, is the RPV(s) (if they're present) and then in the brake valves.

The conventional style MC also requires taking the top off to see how much fluid is in the reservoirs. This lets in dirt, easily dislodges rust flakes around the rim that fall into the MC and it introduces more moisture, from the air, getting into the fluid.

These are all bad things for brake systems and is why on today's vehicles you see MC bodies made from aluminum and the reservoirs are plastic with a much smaller cap on top. You don't have to take the top off a modern MC to see how much brake fluid is inside so, naturally, less dirt and moisture are being introduced into the brake fluid.

I'm currently in the process of switching to front disc brakes on my '69 F-100. I put a new (conventional style) iron MC on my truck a little over 3 years ago, when I went through all 4 drum brakes. I'm not putting the old cast iron MC back on with this front disc swap. I'm replacing it with a modern MC.

Before



Conversion currently in progress.

[motzingg]

^ very interesting about the RPV thing... i've never heard of that before but i've taken them apart and know the part you're talking about.

i'm going to stick with the old style MC for now, but after all the money i've spent on getting my drums up to spec, i definitely would have been better off going right to disc with a new booster and MC and adapting them.

its the old 'throwing good money after bad' fallacy where you've spent so much getting to the point of having operable drums, you don't want to go in and throw away 200-300 bucks worth of brand new parts and go disc. bummer.

either way the drums work pretty damn good and i'm sure with the vac booster set up they will be even better. gotta be careful, if i make it too nice my wife will start wanting to drive it.

[ultraranger]

^ very interesting about the RPV thing... i've never heard of that before but i've taken them apart and know the part you're talking about.

i'm going to stick with the old style MC for now, but after all the money i've spent on getting my drums up to spec, i definitely would have been better off going right to disc with a new booster and MC and adapting them.

its the old 'throwing good money after bad' fallacy where you've spent so much getting to the point of having operable drums, you don't want to go in and throw away 200-300 bucks worth of brand new parts and go disc. bummer.

either way the drums work pretty damn good and i'm sure with the vac booster set up they will be even better. gotta be careful, if i make it too nice my wife will start wanting to drive it.

I understand about being torn on changing out parts, that aren't very old, in order to go in a different direction.

Two days after I bought my truck (4/26/2011), the right rear wheel cylinder blew. I took the top off the (manual brake) MC to find the secondary reservoir was empty and the primary reservoir was only half full of rusty, milky looking brake fluid.

I put the truck up on jack stands, removed all 4 wheels and proceeded to remove all 4 drum brake assemblies. I replaced everything; wheel cylinders, flexible brake hoses, front wheel bearings/seals, front hub dust caps, new spindle nuts, rear axle bearings, axle seals, housing gaskets, all new drum brake shoes, return springs, adjusters and had all four drums turned and bought a new MC (old MC was leaking down the inside of the firewall). All total, I probably had well over $500.00 dollars invested in going through everything.

Roughly 3 years later, I'm removing half of the new components I just replaced not too long ago. The drum brakes maybe have around 6,000-8,000 miles on them. Oh well. Even though the front drums are virtually new, the new discs will be a big improvement and money and time well spent for the upgrade. I've been buying the parts a little at a time for over a year, until I had everything I needed. My cost has been spread out over time so, it hasn't destroyed the bank account in the process.

This is what my '69 F-100's front suspension looked like 3 weeks ago, when I started the front disc brake change over ('77 F-100 front I-beams, radius arms, discs). --I'm also, at this time, adding power steering, a tilt steering column and a front sway bar.





After removing the ugly drum brake parts. --New rotors, bearings, grease seals, spindle nuts, dust caps, flexible brake hoses, newly rebuilt calipers, new brake pads, new shocks, new Moog kingpins/metal kingpin bushings, new Moog CC808 progressive rate coil springs, new Moog tie rods and drag link and new Energy Suspension (black) polyurethane I-beam and radius arm bushings.